Exothermic welding, particularly copper-based aluminothermic welding, is based on reducing copper oxide by metallic aluminum. The reaction is highly exothermic, releasing a large amount of heat, being able to reach temperatures greater than 1000° C. These conditions allow melting the materials to be welded, being joined together by the result of the heat generated by the exothermic reaction.
Although the reaction is chemically aluminothermic, it is known as exothermic welding, conventionally being produced by means of an initiating reactant providing enough energy to activate the process, which takes place rapidly and safely inside a mold, preferably a graphite mold, designed specifically for each element and type of welding, such as, for example, for welding conductors arranged in a T-shape, linearly, in parallel, etc.
There are many advantages involved with exothermic welding since it is a process that results in molecular and not only mechanical bonding of the materials to be welded, assuring the connections not only between copper cables, but also for welding metal strips and parts made of brass, stainless steel, copper clad steel ground rods, etc. In these conditions, welds thus formed have a higher electrical conductivity than that of the conductors themselves, they do not corrode, rust or degrade over time, are resistant to galvanic coupling, able to withstand repeated electrical discharges, the resistance thereof never increases, they are mechanically resistant and more pressure resistant than the conductors themselves, and offer a low resistance connection that is particularly important for achieving a long-lasting and reliable result in forming any ground connection.
The welding material used in exothermic welding is usually a mixture of copper and aluminum powder oxides and metallic alloy-forming elements that are compatible with the elements to be welded. Although the reaction of the welding material does not occur spontaneously, once it is initiated the process is triggered in its entirety without a major energy supply, and molten copper and slag are obtained.
To supply the energy necessary for triggering the exothermic reaction, an initiating reactant powder (initiating material) was conventionally used, said initiating reactant powder having a composition similar to the welding material but somewhat different, especially the aluminum used, which is finer and more reactive, which requires a minimal energy source to react and then transfer to the welding material the energy necessary to initiate the reaction between the metal oxide and the aluminum present in the main reaction. A known sequence for conventional exothermic welding applied to a weld between conductors comprises the following steps:                1. Placing the conductors to be welded in the mold once they are clean and dry.        2. Closing the mold to prevent material leakage and placing a support plate to contain the welding material before the reaction.        3. Pouring the welding material.        4. Pouring the initiating reactant such that about 50% is scattered over the surface left by the welding material whereas the other half is poured in the form of a fuse from the edge of the mold to the welding material for the purpose of facilitating ignition        5. Igniting with a lighter or pistol spark lighter providing enough energy to produce the reaction of the initiating reactant.        6. The energy produced by this reactant triggers the main reaction which is maintained until all the welding material has reacted, melting the support plate, producing molten copper that falls to where the conductors are housed, causing molecular bonding by exothermic welding and the conductors fusing to one another.        7. After waiting a few seconds for the sake of safety, the mold is opened and the weld is obtained, and the mold is cleaned to form, where appropriate, a new connection.        
Conventional methods for exothermic reactions have some drawbacks that were desired to be reduced or eliminated. Therefore, the support plate and the poured welding material powder can present a problem depending on the use conditions or when the mold is deteriorated and the hopper shoot widens. This disrupts plate stability and the welding material passes as powder into the welding chamber, where its reaction will produce slag that does not separate from the molten copper. Furthermore, the suitable arrangement of the initiating material and of the welding material in the crucible hopper or weld mold hopper requires relatively extensive preparation time.
The problems in using and transporting the initiating reactant also make the elimination thereof advisable since environmental conditions (air, temperature, humidity) affect the ease of ignition thereof, whereas due to its chemical characteristics, transport thereof is restricted in some cases and according to importing countries. In the proposed invention, this aforementioned initiating reactant powder (initiating material) is further replaced with a first welding material in a new compact pellet format and with preferred characterizing physicochemical parameters that eliminate the drawback discussed, optimally facilitating and assuring the exothermic reaction with a second welding material mainly in those cases in which said second welding material is also in the form of a solid pellet. Such pellets have the advantage of maintaining the concentration of the entire stationary volume of the reactants preventing problems relating to concentration differences caused by different molecular weights of the components of the welding material.
The attempt has been made to include a container made entirely or partially of a fungible material as a reaction receptacle placed in the weld mold crucible or hopper to overcome one of the drawbacks indicated above. This container containing the welding material powder incorporates an ignition system that eliminates the use of a powder initiator. Therefore, EP1472037 describes an igniter comprising a container having side walls with only the bottom portion thereof being fusible, an exothermic welding material within the container, an igniter extending into the container for igniting the exothermic material and a cover or cap attached to the container sealing the top opening to thereby prevent ingress of contaminants into the welding material, characterized by a refractory material lining the sides walls of the container, wherein the refractory material is a graphite film (foil) which is a separate liner inserted within the side walls of the container, and wherein said side walls of the container have a conical shape and include metal.
Containers of the type described above and the corresponding ignition systems can cause unwanted combustions and residues in the slag or even in the final weld and considerably increase the volume of the product since the container has the same shape as the hopper. The slag that is generated also increases because if the container is not consumed it becomes a residue, and if it is consumed it becomes part of the weld with the composition problems of the molten material which should make the initial mixture change, entailing an additional problem. In turn, if the container is not shaken, over time the heavier components of the mixture could accumulate on the bottom portion of the container, which leads to variations in the partial composition of the welding material affecting the main reaction.
Given its very nature, exothermic welding generates very high temperatures accompanied by a huge release of energy, which can sometimes cause the high-temperature molten material and/or slag to splash out of the weld mold. This presents an occupational hazard inherent to the welding process itself, so the remote detonation or ignition of said process greatly reduces the risks of burns in operators and technicians doing the welding.